An egg a day won't make your health go astray. Photo illustration by Rose Lincoln.

Harvard researchers have unscrambled the egg's rotten reputation among hard-boiled cholesterol watchers: eating an egg a day does not increase the risk of heart disease or stroke, they say.

A team of nutritionists, epidemiologists, and physicians compared the consumption of eggs with the health of more than 115,000 men and women over eight to 14 years, and concluded that healthy people can eat an egg a day without raising their cholesterol to harmful levels.

"We found no significant association between consuming up to one egg a day and risk of coronary heart disease and stroke," Frank Hu, a research associate at the Harvard School of Public Health, told a meeting of journalists at Indiana University on April 20. "We specifically found no evidence for a significant increase with either recent or relatively long-term (over the past decade) egg consumption."

Study participants included more than 80,000 nurses aged 34 to 59 whose diets and health were followed for 14 years, 1980 to 1994. More than 37,000 males -- dentists, pharmacists, and other health professionals -- aged 40 to 75 were followed for eight years, 1986 to 1994. Both the Nurses Health Study and the Health Professionals Follow-up Study are large, long-running investigations conducted by Harvard Medical School and Brigham and Women's Hospital in Boston.

Cholesterol has not been absolved of being a major contributor to fatty deposits that block arteries and cause heart disease and stroke. Most physicians recommend that people consume no more than 300 milligrams of cholesterol a day. Because each one packs 213 milligrams, nutritionists advise most people to avoid more than an egg or two a week.

But the Harvard team, in a report printed in the April 21 issue of the Journal of the American Medical Association, explains the apparent contradiction by noting that eggs contain other beneficial nutrients that may counteract the effects of cholesterol. These nutrients include unsaturated fats, essential amino acids, folate, and other B vitamins.

It is conceivable, they write, that the small adverse effect of an egg on "bad" cholesterol is counterbalanced by potential beneficial effects on "good" cholesterol, and by other nutrients including antioxidants, folate, and unsaturated fat. Good, or high-density, cholesterol protects blood vessels against plaque deposits. Researchers also speculate that eating eggs instead of carbohydrate-rich foods may decrease harmful blood sugar and insulin responses.

This tasty outcome, however, doesn't seem to apply to diabetics. The investigators found consumption of eggs puts diabetics at an increased risk of coronary heart disease. The reason may involve abnormalities in cholesterol transport in the body. The consistency of this finding in the two studies argues against it being a false alarm, the team writes, but "the result should be interpreted cautiously until further research is done."

Hu noted that dietary recommendations to prevent heart disease should concentrate less on cholesterol and total fat intake and more on reducing intake of saturated and trans-unsaturated fats. Saturated fat is found in meats and diary foods, trans fat in margarine, cookies, crackers and fast foods.

"Replacing saturated and trans fats with poly- and mono- unsaturated fats is an effective way to lower coronary heart disease risk," Hu said. "A relatively higher intake of poly- unsaturated fat -- corn or soybean oils -- and mono-unsaturated fat -- olive and canola oils -- actually reduces overall heart disease risk."